I am having a similar issue. We have a TCL Roku TV and have successfully connected and displayed our Nintendo Switch to the tv for over a year and a half. A few weeks ago it stopped working. I only get the Looking for a Signal message.
So far we have tried:
- using a different HDMI cable
- using different HDMI ports
- unplugging all cables and reconnecting in the "proper" order
- Restarting the TV along with #3
- Restarting the TV and Switch along with #3
The one thing I haven't tried is resetting my Roku TV because that is a huge hassle and I get no indication for these support posts whether this actually solves this problem.
Please let me know of any other solutions to this issue, or whether Roku has documented it and is working on a fix.